The present invention relates to medical devices. More particularly, the invention relates to a device made from a less-elastic or biodegradable material that is capable of producing a relatively large radial force in order to prevent device migration and/or maintain patency in a body vessel.
Filtering devices are percutaneously placed in body vessels of a variety of medical patients, including but not limited to trauma patients, orthopedic surgery patients, neurosurgery patients, or in patients having medical conditions requiring bed rest or non-movement. During such medical conditions, the need for filtering devices arises due to the likelihood of thrombosis in the peripheral vasculature of patients wherein thrombi break away from the vessel wall, risking downstream embolism or embolization. For example, depending on the size, such thrombi pose a serious risk of pulmonary embolism wherein blood clots migrate from the peripheral vasculature through the heart and into the lungs. In some cases, a filtering device can be deployed in the vena cava of a patient when, for example, anticoagulant therapy is contraindicated or has failed.
Typically, filtering devices are permanent implants, each of which remains implanted in the patient for life, even though the condition or medical problem that required the device has passed. However, it can be desirable to remove unneeded implants when the medical risk has passed.
In some cases, filters have not been considered removable from a patient due to the likelihood of endotheliosis of the filter or fibrous reaction matter adherent to the endothelium during treatment. After deployment of a filter in a patient, proliferating intimal cells begin to accumulate around the filter struts which contact the wall of the vessel. After a length of time, such ingrowth prevents removal of the filter without risk of trauma, requiring the filter to remain in the patient.
Even in cases where removal of the implant or device is possible, a second surgical procedure and the attendant risks can be undesirable. As such, removal of the device, even when possible, is sometimes not elected.
Medical devices, including filtering devices, can be made from biodegradable materials. These devices have the advantage of functioning for a limited time and then slowly get absorbed by the patient's body, obviating a second surgery for removal of the device. However, unlike permanent devices made from elastic materials like spring steel or shape-memory metals, devices made from biodegradable materials can lack mechanical properties and in some cases make suboptimal contact with vessel walls, thereby risking migration.
It is desirable to use a medical device made of a biodegradable material which can also produce a strong radial force against the wall of a body vessel.